In a general manner, the invention is related to the fields of motion capture, and the geolocating of individuals moving around. Motion capture relates to general-public applications such as leisure applications (interactive games consoles, tracking of sports movements, virtual reality or augmented reality), applications for aiding the navigation of pedestrians (the most widely used at the present time being satellite navigation systems such as GPS), applications for aiding the mobility of vulnerable persons or those temporarily enfeebled by their environment (handicapped persons or those plunged into darkness), and fitness applications (pedometer, calculation of energy expenditure or of distance traveled). Motion capture also relates to medical applications (tracking of the elderly and/or of dependents, analysis of the gait for postural reeducation or aid to diagnosis), safety or rescue applications (locating of firemen inside a building on fire, operational tracking of military servicemen, or surveillance of prisoners), as well as commercially directed applications (statistics on the trajectories followed by consumers in shopping centers or supermarkets, definition of archetypes of use, or proposal of topo-dependent commercial services).
It is notably known to reconstruct the movement of an object or of a person fitted with an object comprising an emitter of signals that are recognized by a satellite-based navigation aid system, such as the GPS system, outdoors, and by a radiolocation system based on Ultra Wide Band (UWB) or WiFi transmissions indoors.
In numerous geographical zones, external or internal, navigation relying on a satellite-based navigation aid or radiolocation system turns out nonetheless to be very tricky, because of the obstruction of the radio signals that are required for the measurement of topo-dependent metrics, for example in the case of unavailability of the signals emitted by one or more satellites of the navigation aid system and required for the measurement of pseudo-distances. In practice, these blockage or obstruction situations heavily degrade the accuracy of the location information, and sometimes even render the navigation aid service unavailable, as illustrated in the document “An evaluation of UWB localization under non line-of-sight (NLOS) propagation” (A. Maali, A. Ouldali, H. Mimoun, and G. Baudoin), published in Wireless Pervasive Computing, ISWPC, 3rd International Symposium on, pages 379-382, in May 2008. Generally, the implementations cited above exhibit a cost, consumption, bulkiness, and/or infrastructure that are unsuitable or indeed crippling for general-public applications.
Other systems are aimed at computing a path on the basis of a given departure point, by using attitude sensors (accelerometer(s), magnetometer(s), gyrometer) usually delivering inertial measurements. These measurements make it possible to undertake navigation by more or less accurate and complicated means, such as described, for example in the documents “Inertial head-tracker sensor fusion by a complementary separate-bias kalman filter” (E. Foxlin) published in March 1996 in Virtual Reality Annual International Symposium, Proceedings of the IEEE 1996, pages 185-194; “Detection of spatio-temporal gait parameters by using wearable motion sensors” (K. Kogure L. Seon-Woo, and K. Mase), published in 2005 in Engineering in Medicine and Biology Society. IEEE-EMBS 2005. 27th Annual International Conference of the, pages 6836-6839, 2005; “Pedestrian tracking with shoe-mounted inertial sensors” (E. Foxlin), published in November 2005 in Computer Graphics and Applications, IEEE, 25:38-46, November-December 2005; or “Integration of foot-mounted inertial sensors into a Bayesian location estimation framework” (P. Robertson B. Krach), published in March 2008 in Positioning, Navigation and Communication, 2008. WPNC 2008. 5th Workshop on, pages 55-61. Such systems are of high cost and complexity, and often lack accuracy.
Video games consoles, such as the Wii, use optical and/or ultrasound sensors to determine the trajectory of a game control element. These systems are expensive and limited.
There also exist, as presented in the documents “Assessment of walking features from foot inertial sensing” (S. Scapellato F. Cavallo A. M. Sabatini, and C. Martelloni), published in March 2005 in Biomedical Engineering, IEEE Transactions on, pages 486-494, or “Multisensor approach to walking distance estimation with foot inertial sensing” (D. Alvarez A. M Lopez J. Rodriguez-Uria J. C. Alvarez, and R. C. Gonzalez), published in August 2007 in Engineering in Medicine and Biology Society, 2007, EMBS 2007. 29th Annual International Conference of the IEEE, pages 5719-5722, systems which assume two accelerometers and a gyrometer which are disposed in the sagittal plane of a user, making it possible to determine the attitude of this sensor in the plane. The acceleration is integrated on the axis of the foot. These systems have a reduced cost, but present other drawbacks. On the one hand, they assume that the sensors are perfectly placed in the sagittal plane, this being almost impossible for the user to actually achieve, and causing an estimation error related to the poor positioning of the sensor or sensors. On the other hand, they assume that walking takes place in the sagittal plane, which may not be the case, when walking sideways on, for example.
The document, “An innovative shoe-mounted pedestrian navigation system” (K. Fyfe, Gérard Lachapelle, R. Stirling, and J. Collin), published in April 2003 in Proc. European Navigation Conf. (GNSS), CD-ROM, Austrian Inst. of Navigation, discloses a system fitted with three accelerometers and with a fourth accelerometer so as to calculate the angle undergone by the sensor. This further accelerometer is placed on the same mobile element, but some distance from the latter. The two sensors therefore see the same rotation and the same displacement. Such a structure makes it possible to estimate the speed of rotation of the mobile element, in rotation about a substantially constant direction, while dispensing with a gyrometer. This system has a reduced cost due to the replacing of a single-axis gyrometer with a pair of accelerometers with respect to the systems with gyrometers proposed by Alvarez et al. and Scapellato et al. However, such a system exhibits the same drawbacks as the example cited hereinabove, since only the rotation about the axis orthogonal to the sagittal plane is taken into account. Furthermore, the estimation of the rotation by a pair of accelerometers, just like that carried out with the aid of a gyrometer, exhibits significant drifts. A heading is also determined with the aid of a magnetometer, for example when the foot is resting, thus giving the direction of the foot and not the sought-after direction of the displacement.